Railroad maintenance is one of the greatest problems facing the transportation industry today. It is estimated that annual costs related to cracked railroad wheels is at least $24 million. This problem of cracked railroad wheels continues to grow. Estimates are that there at least 5% more cracks per year while other sources estimate that there may be 12% to 15% more faults with respect to railroad wheels per year.
There are several types of defects with respect to railroad wheels, the primary ones being, thermal cracks, vertical split rim and shattered rim cracks. Thermal cracks, which include tread and flange tip cracks, account for approximately 8,000 to 10,000 wheel replacements every year. Shattered rim cracks account for another 300 to 500 wheel replacements per year.
As shown in FIG. 1, thermal cracks 6 occur on the tread 12 and flange 2 of a typical wheel. Additionally, a shattered rims 8 and vertical split 10 can be seen in FIG. 1.
It should be noted that other than by visual inspection, no technique is readily available today to perform inspections on railroad wheels while they are still mounted on trains. Prior acoustic inspection techniques have proven to be unreliable and generally limited to surface thermal crack detection, as described in the U.S. Pat. No. 3,812,708,
Most conventional testing systems use a contact system whereas the laser air hybrid ultrasonic technique (LAHUT) system as described in U.S. Pat. No. 6,862,936 is a non-contact system.
What is needed is a robust system that can reliably detect flaws in railroad wheels while the train is in operation.